1. Field of the Invention
The present invention relates to a device and a method for determining knocking of an internal combustion engine. In particular, the invention relates to a technique of determining whether knocking has occurred or not using a value that is corrected according to the magnitude of vibration of the internal combustion engine.
2. Description of the Background Art
Various methods for detecting knocking (knock) occurring in an internal combustion engine have been proposed. For example, a technique determines that knocking has occurred when the magnitude of vibration of the internal combustion engine is larger than a threshold value. There is a case, however, where the magnitude of such noise as vibration which occurs when an intake valve or an exhaust valve for example closes is larger than the threshold value while knocking does not occur. In this case, although knocking has not occurred actually, it could be erroneously determined that knocking has occurred. Accordingly, a technique has been proposed that determines whether knocking has occurred or not based on the waveform of vibration for considering such characteristics other than the magnitude as the crank angle at which vibration occurs and the damping rate.
A knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-021032 includes: a knock sensor detecting knocking in an internal combustion engine; a statistical processing portion statistically processing an output signal detected by the knock sensor; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the output signal detected by the knock sensor; and a final knock determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final knock determination portion finally determines that knocking has occurred. The first temporal determination portion makes a comparison between the maximum value of the output signal detected by the knock sensor and a knock determination level (knock determination value) calculated based on the result of processing by the statistical processing portion to determine whether or not knocking has occurred. The knock determination value is corrected, based on the frequency of occurrence of knocking, to a value determined by subtracting a set value ΔV from the knock determination value or to a value determined by adding to the knock determination value the product of a value A larger than “1” and set value ΔV.
When the knock determination value is corrected, it is not preferable that the knock determination value is corrected without limitation. This is for the reason that the magnitude of vibration occurring in the internal combustion engine varies depending on the condition of the engine itself and the drive environment and thus the corrected knock determination value is not necessarily appropriate all the time. Therefore, if an extreme correction is made, the knock determination value is too large or too small with respect to the magnitude of vibration occurring in the internal combustion engine, resulting in deterioration of the precision with which the determination is made as to whether or not knocking has occurred, contrary to the intention. Japanese Patent Laying-Open No. 2003-021032, however, is silent about restricting the knock determination value.